The present invention relates to a hydrodynamic bearing provided with a low friction metal layer having water repellency on a surface of the bearing, a hydrodynamic bearing apparatus, a fabrication method of a hydrodynamic bearing and a bearing surface working method providing a low friction metal layer on a surface of the bearing.
With high speed formation of information processing or image processing in recent years, there has been used a hydrodynamic bearing apparatus in a drive motor for driving a rotating member such as a polygon scanner motor apparatus or a disk apparatus and there are requested a small-sized and solid constitution, high durability and stable high-speed rotation thereof.
In order to meet the request, for example, as shown by FIG. 6, there is disclosed an invention in which a rotating member 3, a fixing portion 5 and a rotating shaft 9 fixedly attached to the fixing portions 5 are constituted by a ceramic material in Japanese Patent Laid-Open No. 241516/1988. According to the apparatus of the related art, the rotating member 3 having a multiple face mirror (polygon mirror) is provided rotatably relative to the fixing shaft 9 provided at the f fixing portion 5 and there are provided a magnet 13 provided to the rotating member 3 and an armature 11 having a stator coil for rotating the rotating member 3 opposed to the magnet 13.
Further, there is formed a dynamic pressure generating groove at either of bearing faces of the rotating member 3 opposed to the fixing portion 5 and the fixing shaft 9 and bearing faces formed at the fixing portion 5 and the fixing shaft 9 opposed to the rotating member 3 and the fixing portion 5 rotatably supports the rotating member 3 by pneumatic dynamic pressure, however, there poses a problem in which it is extremely difficult to work the dynamic pressure generating groove at the ceramic material finely and without increasing fabrication cost.
Hence, in order to resolve the above-described problem, there is provided a hydrodynamic bearing using light metal which is inexpensive and having excellent workability in place of the above-described ceramic material. For example, in the case of a hydrodynamic bearing used in a rotating multiple face mirror apparatus, adoption of an aluminum material is preferred, since there is achieved an advantage as the same material is used for the multiple face mirror made of an aluminum alloy including an advantage against a change in temperature. Further, in order to promote wear resistance of an aluminum material, there is known a constitution in which there is carried out Nixe2x80x94P electroless plating including small particles of SiC on a surface of a bearing or a constitution in which a low friction resin layer is coated thereon.
However, according to the constitution of carrying out the Nixe2x80x94P electroless plating including small particles of SiC on the surface of the bearing, irregularities remain on the surface of bearing. Further, in the case of a hydrodynamic bearing having a clearance of about 2 through 6 xcexcm, such irregularities of the surface deteriorates dynamic pressure effect and accordingly are not preferable. Further, since friction force is comparatively large, there poses a problem of wear or dust formation by contact of the bearing faces when a motor is started or stopped.
Meanwhile, in the case of the constitution in which the low friction resin layer is provided by the Nixe2x80x94P electroless plating including small particles of SiC, the irregularities of the surface are inconsiderable and accordingly, loss of the dynamic pressure effect thereby can be reduced, however, conversely, there poses a new problem in which the bearing faces are liable to adsorb each other by dew condensation since conversely, there are no irregularities. Further, the hardness is insufficient and it is difficult to completely resolve the problem of wear or dust formation. Further, there also poses a problem that static electricity is liable to store in a rotating member since there is no electric conductivity. In addition thereto, in the case of coating of resin, it is difficult to control a thickness of the resin layer, there is needed a step of preparing and selecting a member used integrally therewith having several stages of sizes or a step of coating the resin previously thickly and thereafter cutting the resin to a predetermined thickness and accordingly, time and labor are taken.
Hence, it is an object of the present invention to provide a hydrodynamic bearing, a hydrodynamic bearing apparatus and a fabrication method of a hydrodynamic bearing and realize a bearing surface working method capable of resolving the above-described problem.
The invention achieves the above-described object by providing a hydrodynamic bearing comprising a fixing member fixed to a side of a stator, a rotating member fixed to a side of a rotor capable of rotating relative to the stator and opposed to the fixing member via a fluid, and hydrodynamic pressure generating means for generating a dynamic pressure by the fluid between the rotating member and the fixing member in rotating the rotor, wherein in at least one of the rotating member and the fixing member, a surface thereof opposed to other thereof is a low friction metal layer having water repellency (first constitution of the invention).
The invention resolves the above-described problem by providing the low friction metal layer having water repellency on the surface of the bearing of the hydrodynamic bearing. That is, by providing the low friction metal layer, friction can be reduced and wear or dust formation can effectively be restrained. Further, by providing the metal layer having water repellency, condensed dew can be avoided from being stored, occurrence of adsorption between the rotating member and the fixing member by dew condensation can be prevented and corrosion by dew condensation can be prevented.
The low friction metal layer having water repellency can be formed by plating. Further, a layer thickness of the low friction metal layer having water repellency can strictly be controlled by controlling concentrations of respective components of a plating solution, a plating time period and temperature and can be restrained in a strict predetermined tolerance set in the rotating member and the fixing member of the hydrodynamic bearing.
Further, the low friction metal layer is provided with excellent conductivity and accordingly, static electricity can be avoided from staying.
With regard to the layer thickness of the low friction metal layer having water repellency, although depending on an apparatus of adopting the hydrodynamic bearing, in order to achieve low friction performance and water repellency while restraining a dispersion in the layer thickness within a predetermined tolerance which does not influence on the dynamic pressure, the layer thickness is preferably 0.2 through 20 xcexcm and more preferably 5 through 10 xcexcm.
The invention can be constituted by the hydrodynamic bearing in which the low friction metal layer having the water repellency is constituted by dispersing very small particles realizing the water repellency and the low friction performance in a metal base in the hydrodynamic bearing of the first constitution (second constitution of the invention).
In order that the very small particles are dispersed substantially uniformly in the low friction metal layer, the low friction performance and the water repellency are achieved uniformly in the low friction metal layer and irregularities having a size which influences the dynamic pressure are not produced, the particle size is preferably 0.01 through 10 xcexcm and more preferably 0.1 through 0.5 xcexcm.
As the metal base, Nixe2x80x94P, Nixe2x80x94B, Nixe2x80x94Coxe2x80x94P, Ni, Nixe2x80x94Co, Co, Nixe2x80x94W or Cr can be used.
According to the hydrodynamic bearing of the second constitution, in one of the rotating member and the fixing member, a surface thereof opposed to other thereof is the low friction metal layer having water repellency constituted by dispersing very small particles realizing water repellency and low friction performance in a metal base and other can be constituted by a metal layer comprising a metal base similar to the low friction metal layer.
In this way, by dispersing the very small particles to the surface of the one opposed to the other of the rotating member and the fixing member and constituting the other by the metal layer of a similar metal base, wear of surfaces opposed to each other can be reduced further effectively.
Further, the invention can be constituted by the hydrodynamic bearing in which the very small particles are very small particles of a fluorine compound in the hydrodynamic bearing of the second constitution (third constitution).
As the small particle of the fluorine compound, there can be used a very small particle comprising at least one of PTFE (polytetrafluoroethylene), FEP (tetrafluoroethylene-hexafluoropropylene copolymer), PFA (tetrafluoroethylene-per-fluoroalkylbiphenylether copolymer), PCTFE (polychlorotrifluoroethylene), ETFE (tetrafluoroethylene-ethylene copolymer) and graphite fluoride and a mixture of a plurality of kinds of the very small particles. These particles are excellent in self lubricity, nonadherence, slidability (low friction performance), water repellency and oil repellency and are used preferably, particularly, the particle of PTFE is used further preferably.
Further, the present invention provides the hydrodynamic bearing in which the hardness of the low friction metal layer falls in a range equal to or larger than Hv600 and equal to or smaller than Hv1000 and the friction coefficient is equal to or smaller than 0.25 in the hydrodynamic bearing according to any one of the first constitution through the third constitution (fourth constitution).
In the hydrodynamic bearing according to any one of the first through the third constitutions, there can be formed the low friction metal layer having the hardness of Hv600 through 1000 and the friction coefficient equal to or smaller than 0.25. Further, the low friction metal layer having the hardness equal to or larger than Hv600 and the friction coefficient equal to or smaller than 0.25, maintains excellent wear resistance and durability against contact of the rotating member and the fixing member in accordance with starting and stopping to rotate the rotor and shows water repellency against dew condensation. Further, the low friction metal layer is preferably provided with the hardness equal to or smaller than Hv1000.
The invention achieves the above-described object by providing the hydrodynamic bearing apparatus having a stator, a rotor rotated relative to the stator and the hydrodynamic bearing having any one constitution of the first constitution through the fourth constitution (fifth constitution).
According to the hydrodynamic bearing apparatus of the fifth constitution, by adopting the hydrodynamic bearing having any one constitution of the first constitution through the fourth constitution, wear or electrification of the hydrodynamic bearing is restrained, corrosion by dew condensation is prevented and wear resistance and durability are promoted. Further, there can be prevented occurrence of adsorption between the rotating member and the fixing member by dew condensation and an increase in power consumption in starting by the adsorption can be restrained.
The invention achieves the above-described object by providing a method of fabricating a hydrodynamic bearing comprising a plating step of forming a low friction metal layer having water repellency constituted by dispersing very small particles realizing the water repellency and low friction performance in a composite plating metal base including at least one of phosphor and boron in at least one of base members of the rotating member and the fixing member on a face thereof opposed to other thereof by an electroless plating, a hardening treatment step of hardening the low friction metal layer by heating the one base member at predetermined hardening heat treatment temperature after the plating step, a stress relieving step for relieving stress of the base member by heating at temperature equal to or higher than the hardening heat treatment temperature of the hardening treatment prior to the plating treatment, and an integrating step of integrating the one and the other in a state in which the low friction metal layer of the one is opposed to the other and a hydrodynamic pressure can be generated between the one and the other (sixth constitution).
In the method of fabricating the hydrodynamic bearing according to the sixth constitution of the invention, the low friction metal layer is formed by the electroless plating and accordingly, the low friction metal layer having substantially uniform thickness can be formed, which is useful in a hydrodynamic bearing in which an error in the layer thickness needs to be controlled strictly.
Further, as the metal base, there is used a composite plating metal base including phosphor or boron and by heating after plating, the low friction metal layer having high hardness can be formed. Further, in the stress relieving step prior to the plating step, stress is relieved under temperature environment at hardening treatment temperature or higher and accordingly, deformation caused by the hardening treatment after the stress relieving step can be prevented.
The invention achieves the above-described object by providing a method of working a surface of a bearing for providing a low friction metal layer having water repellency on the surface of the bearing of a hydrodynamic bearing rotatably supporting a rotor, the method comprising an electroless plating step of forming the low friction metal layer including very small particles realizing the water repellency and low friction performance by an electroless plating on the surface of the bearing of the hydrodynamic bearing and a hardening heat treatment step of hardening the low friction metal layer by setting hardening heat treatment temperature to be equal to and higher than 200xc2x0 C. and equal to and lower than 400xc2x0 C. (seventh constitution).
In this way, in the hardening heat treatment step, by setting the hardening heat treatment temperature to be equal to or higher than 200xc2x0 C. and equal to or lower than 400xc2x0 C., there can be realized the hydrodynamic bearing having the low friction metal layer having the hardness and the friction coefficient of the fourth constitution.